I went hiking in the hills in Simi Valley which is on the border of Los Angeles County but it is in Ventura County in Southern California. In the hills there is an abandoned golf course with a small lake or pond. There are swallow or swift type looking birds swooping around close to the water and I have no idea what type of birds these are. I have searched and looked at my bird books with no success.
The bird is mostly black with white around its neck and a white stomach. This is the only photo I was able to get because they flew very fast.